Black oxide stainless fasteners to reduce galling in stainless holes?

maxh · Aug 20, 2011

We have a customer that brings us a stainless part from time to time with a stainless screw broken off in it for us to fix. Galling is the nature of the stainless on stainless beast, but they don't feel like they can change either material, nor use anti-seize compound.

However, I've noticed that McMaster sells some 18-8 SS fasteners with a black oxide finish which they say "provides lubricity and an attractive, matte-black finish." Does anybody have experience with these, and do you think they'll provide any significant reduction in galling when used in stainless holes?

WaterFXMatt · Aug 20, 2011

I have used them and after a few uses...the coating waers off and you have same problem.

Anti seize is the only way to go. Swagelock Blue Goop is what I would recomend, and if they need a NSF listed food safe material, they also make a white veriosn that is food safe and listed.

Dave Cross · Aug 20, 2011

I've only had luck with anti seize as well, I think Permatex makes the foodsafe stuff we use.

jim rozen · Aug 20, 2011

Another approach, one used widely in the high vacuum community, is to have the
stainless screws gold-plated.

Seriously, it works. Gold provides great self-lubrication. They won't gall.

jkilroy · Aug 20, 2011

Get out the goop. White lithium grease works well, as does loctite, if you are using that as well. Number one rule, put away the air wrenches, turn down by hand.

jdj · Aug 20, 2011

maxh said:
We have a customer that brings us a stainless part from time to time with a stainless screw broken off in it for us to fix. Galling is the nature of the stainless on stainless beast, but they don't feel like they can change either material, nor use anti-seize compound.
?

If they had to get them out themselves, they MIGHT rethink those factors. Hell, they should ANYWAYS! Have they ever heard of the dry, spray graphite/moly stuff? As someone else mentioned, they DO make food-safe anti-seize! I know that there are applications where you REALLY can't use something on the threads, but how common do you REALLY think those are? Call me crazy, but I don't think they are that common. This dumb-ass must just like an excuse to come over and see you!

Jeff

Close Work · Aug 20, 2011

I second the suggestion of gold plating. Widely used in vacuum systems. You might be able to buy gold plated screws but having them plated isn't that hard to do and you can also plate them yourself. Gold plating is fairly simple to do. Just don't lick your fingers after getting in the solutions.

maxh · Aug 20, 2011

It's a semiconductor application, so food safe still isn't good enough. They don't want any material that may contaminate the process. I think I'll quote them supplying the black oxide SS screws in a use-once-then-throw-away quantity (I'll have to cut them to length as McMaster doesn't stock the needed length,) as well as the gold plated option. Thanks for the feedback!

Keith Krome · Aug 21, 2011

Gold? Are you guy's rich? We have silver plated fasteners for the high vacuum stuff I've seen.

Regarding black oxide on stainless, I'm not sure of the exact nature of the coating (oxide), but I've heard that black oxide on stainless can cause corrosion troubles, in that the black oxide actually provides less protection that the natural oxide that occurs on stainless.

Edit: Here is a link on fasteners and coatings:

http://www.designnotes.com/companion/manual-1.html

Fasto · Aug 21, 2011

If you can figure out why the SS fastener was spec'd you might be able to suggest a better alternative such as titanium. The single-use black oxide fastener also sounds reasonable.

specfab · Aug 21, 2011

I use an outside process for some 303 stainless optical assemblies that is done by Dicronite. This is a high-pressure spray application (as I understand it) of a dry powder that embeds and bonds to the material surface. We have a high-precision 0.5mm pitch thread fit with about .001" clearance on PD for a ~ 30mm diameter threaded barrel, which can't tolerate any lube creep or particulation, and needs to be tight when adjusted correctly, but also adjustable later. Don't know if this will help you, but might be worth looking into. The black oxide as noted will wear away easily.

Dicronite Dry Lubrication

No connection, just an occasional customer.

CBlair · Aug 21, 2011

So if I understand it correctly the Dicronite is not a product you apply but a process you send your parts for?

Charles

USMCPOP · Aug 21, 2011

From the Dicronite site: [FONT=Arial, Helvetica, sans-serif]The semiconductor equipment industry utilizes Dicronite dry lubrication to address challenging issues in precision tolerances and vacuum operating conditions under cleanroom environments. [/FONT]

jim rozen · Aug 21, 2011

We have silver plated fasteners for the high vacuum stuff I've seen. "

The silver does tarnish if exposed to air often, as some of these systems are.
The money is all in the labor, first off. And the gold-plating is done in-house,
with 'funny money' transferred between departments. And the department
that does that, is not set up to do wet electroplating of silver, but are set up
to do gold.

Sounds nuts I know but it's the cheapest way for folks in house to get
the performance they need.

Winterfalke · Aug 21, 2011

Just as a side note, the galling between stainless fasteners seems worse when the parts are all the same alloy, so making sure the part, bold, and/or nut are all different alloy types can sometimes get a little more life out of them.

jdj · Aug 21, 2011

maxh said:
It's a semiconductor application, so food safe still isn't good enough. They don't want any material that may contaminate the process.!

I think they need to look at what constitutes "contamination" in reality, not fantasy-land. I guess they as so many other people don't care about common sense. Technically, everything is and always will be "contaminated".

Jeff

ZAGNUT · Aug 21, 2011

don't know where they're from or why i even have them but somewhere amongst my junk is a handful of stainless torx head screws that have been TiN coated up to the bottom of the head. maybe to prevent galling?

specfab · Aug 21, 2011

CBlair: Yes, the Dicronite process/application is done by the vendor, in my case Dicronite Southwest. I haven't explored whether there are competing similar processes, using perhaps a chemically similar material; we have been reasonably satisfied with the results so far.

4GSR · Aug 21, 2011

Send them to Tool-Flo in Houston and have TiN coating put on them. That's what a high end custom gun manufacture does.

Ken

Mark Leigh · Aug 21, 2011

jkilroy said:
Get out the goop. White lithium grease works well, as does loctite, if you are using that as well. Number one rule, put away the air wrenches, turn down by hand.

AMEN to the no power driven tools, they just make threads get hot faster !

Black oxide stainless fasteners to reduce galling in stainless holes?

Hot Rolled

Plastic

Titanium

Diamond

Diamond

Diamond

Cast Iron

Hot Rolled

Stainless

Hot Rolled

Titanium

Diamond

Titanium

Diamond

Stainless

Diamond

Hot Rolled

Titanium

Diamond

Stainless

Similar threads